Glidobactin is a complex of novel antitumor antibiotics elaborated by Polyangium brachysporum sp. nov. No. K481-B101 (ATCC 53580). The three major components, glidobactins A, B and C have been isolated and their chemical and biological properties characterized. They are unique acylpeptides structurally unrelated to any previously known antibiotics. In our further investigation of the metabolites, five related congeners named glidobactins D, E, F, G and H were found as co-products of the major glidobactins A, B and C. Glidobactins D, E and F differ from glidobactin A only in their fatty acid side chains, while glidobactin G contains a hydroxymethyl group on the 12-membered core ring in place of the methyl group of the other glidobactins. The structure of glidobactin H has not yet been determined. This communication presents the isolation, properties, structures and biological activities of the new components.